The Monster Within Me
by Bamimilyt6
Summary: Chara has been in control. She reset the timeline. She possessed Frisk. She killed everyone. But while battling Sans, Frisk regains the determination to resist Chara. But will she be able to gain control before Chara resets again? Female!Frisk and Female!Chara. I don't own the picture used for the title page! Oneshot. Rated just in case.


**Hey guys! Surprise, another story even though I have other ones that are unfinished! I switch fandoms too often. It's a problem.  
** **I've gotten into Undertale recently, so I decided to write this little one shot I thought of while reading other Undertale fanfics.  
I hope you like it! Sorry if any characters seem OOC...**

 **~Emily Believes xoxo**

* * *

 _The timeline had been reset. Frisk knew. One moment she was surrounded by all of her new friends on the surface, the next she was surrounded by a small patch of golden flowers. In fact, she had fallen on those exact flowers when she first entered the Underground. ...Was she really back to the beginning? And if so… who brought her there?_

 _It couldn't have been Flowey, and he was the only other person (er, living being) that had the power to save and reset, at least that she knew of. (Besides herself, of course, but she knew she didn't bring herself here.) He had a soul now. He had compassion, love, mercy… There was no way he would reset the timeline. Not now, anyways._

" _Hello!" she heard a voice say, expecting it to be Toriel or Flowey, only to turn around to see someone else. It was a girl, roughly her age, with daunting red eyes and a green sweater that had a single a yellow stripe in the middle. Even though her eyes were a dark, blood red, she carried a friendly smile. "You seem lost. Don't worry, I can show you around! My name's Chara!" She held out a helping hand._

 _Frisk was cautious; this girl reminded her of Flowey somehow, the old Flowey. The soulless Flowey. The evil Flowey. And didn't Asriel (who, it turns out, was Flowey before he was a flower) mention someone named Chara? Isn't that who he mistook Frisk for, or at least who he wanted to believe Frisk was? She had to admit, they looked rather similar._

 _Hesitantly, she grabbed Chara's hand. She didn't know whether she was surprised or not that the girl pulled her up instead of pushing her to the ground. Maybe she wasn't so bad. After all, she had a genuine smile on her face. Just as Frisk was about to open her mouth to thank her, Chara swiftly jabbed her hand towards Frisk's neck, grasping it tightly, causing Frisk's breath to hitch sharply._

" _You_ idiot _!" Chara spoke, showing a knife that she had been holding all along. The smile on her face managed to twist into a smirk so quickly. "Here, let's play a game! I like games!" She pressed the tip of the knife against Frisk's chest. "I'll play the killer! You can be the victim!" Chara applied continuous pressure on the blade, and it soon ripped a small hole in Frisk's sweater. "The rules are simple! I'll kill you, absorb your soul, and then kill everyone you love and care for while you get to watch, not being able to save them! It'll be fun!"_

 _The next move Chara made movement was swift. She thrusted her knife into Frisk's chest before she had time to react, causing her the fall to the ground. Then, Chara saw it: Frisk's soul. She quickly grabbed it before it shattered._

 _She knew she only had one option. Since humans couldn't absorb other humans' souls, she had to possess Frisk. Take over her body. This would resurrect Frisk, however, but that was all the better. She could watch her friends die without being able to save them._

 _After all, Chara was in control now._

 _She felt her body slowly fade away as her mind grew connected to Frisk's soul._ Clang _. The knife dropped to the ground as only one vessel was left in the room. Frisk. But it was no longer Frisk. She had murderous red eyes instead of innocent brown ones, for she was no longer in control. It was Chara._

 _It was only the beginning. Chara picked up her knife with Frisk's hand upon hearing footsteps. Toriel's footsteps. Soon, a goat-like monster in a purple and white dress stood in front of her, someone she used to call "mom." The woman looked like she had rushed down to the flowerbed, as a worried look was written on her face. But none of that stopped Chara from quickly slashing Toriel across the face the instant she saw her._

" _No! Toriel!" she heard Frisk exclaim in the back of her mind. The outburst was filled with pain. Another cry was emitted once Toriel's entire body disappeared into dust. But the desperate and foolish attempt to call back the merciful, motherly woman was never made audible._

 _Nobody heard. Nobody came._

 _Chara's plan was working perfectly. Every monster killed, every monster turned to dust… She knew it was emotionally damaging Frisk, a kind-hearted girl who made the mistake of befriending them. Countless times she could tell Frisk was trying to stop the genocide, especially when Chara encountered her good friends. She tried to gain control over Chara while exclaiming her disbelief of the situation._

" _Toriel! Wait… huh, how…? No… No, no, no, no, no! No! Toriel! Toriel… M-Mom…"_

" _No… No! Not Papyrus! NO! He doesn't deserve it! He… He didn't deserve it…"_

" _C'mon Undyne, you can defeat… defeat this monster… You have to stop this… NO! Undyne! Chara, just STOP! Stop NOW!"_

 _Frisk had lost her hope. She had lost her determination. She couldn't beat Chara. She couldn't regain control. She had reluctantly accepted the fact that Chara was going to kill everyone. It was hopeless to try and resist such notions anymore._

 _And next… and next was… next had to be Sans._

* * *

Chara walked into the Judgement Hall, covered in blood and monster dust from past battles. She walked slowly into the gold and white room, holding her knife out in front of her in case there was anyone standing around, preparing to attack...

"Heya."

She quickly turned around, seeing a short, big boned skeleton that had on a blue coat, shorts, and… were those slippers? Surely he would be easy to defeat. "Good luck Sans," she heard Frisk whisper, but the statement sounded so hopeless, devoid of any sort of confidence. It was meek, almost. This caused Chara to smirk.

"You've been busy, huh?"

Chara raised an eyebrow. Of _course_ she had been busy. Where would nearly everyone and everything in the Underground be otherwise? Her lack of an answer caused an eerie silence between the two. The only sounds heard were the echoing of Chara's footsteps as she advanced forward ever so slightly.

Sans continued, "So, I've got a question for ya. Do you think even the worst person can change? That everyone is a good person, even if they try?"

"Yes," Frisk said, but Chara simply stayed silent. She had to focus. She couldn't let herself get drawn into his tricks.

"Heh, heh, heh, heh… Well, here's a better question. Do you wanna have a bad time? 'Cause if you take another step forward, you are REALLY not going to like what happens next."

Chara, as if testing the seemingly harmless, lazy skeleton's words, she lifted her left foot and placed it a pace or two in front of her, bringing her other foot up to it and glancing up at Sans. "Welp," he said. "Sorry, old lady." His left pupil suddenly gained a cyan iris, while the other disappeared. Both Frisk and Chara were shocked by this. "This is why I never make promises."

The room grew dark, almost pitch black. A small area in the room surrounding Chara and Sans was illuminated. Chara grew confused when saw she Sans - her enemy, the only one standing in between her and the King, the next victim - standing there with his hands behind his back and his eyes (well, eye sockets) closed. She furrowed her eyebrows. What was he playing at? "It's a beautiful day outside," he said. "Birds are singing, flowers are blooming… On days like these, kids like you…"

Immediately when he paused, Chara saw the real danger in this enemy. There was a cyan light of shorts that quickly grew around his left hand. Bones were sent flying in her direction. She could tell that he had missed, so she stood idly by, waiting for another attack, but without her control she was sent crashing into the bones. "Argh!" Chara exclaimed, both in pain and in frustration, as she collided with the bones. She saw her HP drain even after the initial hit. Four skulls - cow skulls, if she had to guess - appeared beside his head. It only took her a few seconds to realize that those skulls were blasters, and they sent large, white beams at her, which was a direct hit as well. Her HP drained even more as more bones and beams came flying in her direction, until eventually…

Zero. Her HP had drained to zero in only a few attacks. _Reset, reset, reset…,_ Chara thought after she felt Frisk's soul shatter.

"... _should be burning in Hell_."

Quickly, she pressed the reset button, and she found herself back at the entrance of the Judgement Hall. "You'll never defeat Sans!" Frisk said confidently, but Chara quickly brushed it off. _Ridiculous_ , she thought, _I was just distracted before._

Chara approached Sans once more. Sans looked at her almost quizzically for a brief moment before regaining his usual smile. "Heya," he said. "You look frustrated about something. Guess I'm pretty good at my job, huh?" Wait, he didn't say that before. Did… Did he know when the timeline was reset?

He reenacted the same attack he did before the reset, and Chara had managed to dodge all of it. Any hope Frisk had gained after the first short battle, if any at all, vanished. When it was her turn, Chara quickly tried to make a killing jab, but to her surprise, he moved to the side. No other enemy had done so. "What, you think I'm just going to stand there and take it?" he rhetorically asked.

He moved back to his original spot shortly after. "Our reports showed a massive anomaly in the spacetime continuum. Timelines jumping left and right, stopping and starting…" In the middle of his explanation, he unleashed another bone-themed attack on Chara, which she swiftly dodged. "...until suddenly, everything ends." The Gaster Blasters suddenly sent large beams soaring in her direction, and she couldn't manage to duck before she was hit multiple times. "Heh, heh, heh… that's your fault, isn't it?" she heard him say right before, once again, Frisk's soul shattered.

 _Ugh!_ Chara thought right before resetting again. _This is going to be harder than I thought..._

* * *

Eighteen times. Eighteen times she went to battle with this Sans character. Eighteen times she had to reset because of his stupid flying bones and strange skull blasters that were practically unavoidable, in her opinion. And _God_ , he was annoying. She could hardly focus on the fight with all of his side commentary and stories!

And as if it couldn't get any worse, the more Chara had died, the more Frisk grew determined. And with enough determination, she could…

 _No! I'm in control!_ Chara frustratingly reminded herself. _She can't take over!_

She had come too far, too far to go back and start from the beginning again. Chara stared at the cyan glow around Sans's left hand. Just after he threw another bone attack, he looked into her dark red eyes and started talking again, causing Chara to momentarily to break from her fighting stance and roll her eyes. "I know you didn't answer me before, but... somewhere in there... I can feel it. There's a glimmer of a good person inside of you." _Oh no_ , Chara thought as Frisk gasped. "The memory of someone who once wanted to do the right thing. Someone who, in another time, might have even been... a friend?"

"Yes!" Frisk exclaimed. "He knows about the resets… and he remembers me! You can't win, Chara!"

 _I always win,_ she telepathically reminded Frisk. _It isn't over yet._

"C'mon, buddy. Do you remember me? Please, if you're listening... Let's forget all of this, ok? Just lay down your weapon, and... well, my job will be a lot easier."

But Chara never put down her weapon. _I've come too far… I've come too far to give up now…_ But she could tell that Frisk was actively trying to gain control, trying to at least drop the knife…

"Welp," Sans said after a few seconds, "it was worth a sh-"

 _Clang_. The knife was tossed aside, but strangely, the girl almost immediately tried to run back to retrieve it, before randomly falling to her knees.

"I… WON'T… LET… YOU… WIN!"

Sans raised an eyebrow. The outburst wasn't aimed at him. If anything, it was as if she was talking to herself. Suddenly, she looked at him, her eyes noticeably brown instead of red. Her demeanor had completely changed in a matter of seconds, like she was a different person. "Sans!" she said. Her voice… it sounded familiar.

This couldn't be the one who kept resetting, the one who kept fighting him, the one who so desperately wanted to kill him… It had to be the girl from another timeline… somehow.

"Sans! I don't want to kill anyone! There's this girl named Chara who keeps resetting the timeline! She possessed me and killed everyone! I come from a timeline where we made it to the surface… and Flowey wouldn't reset anything because he gained a soul! He's not evil anymore! Not in my timeline! Please, Sans… Let me fix this. Kill me… Kill me and I'll handle Chara. We'll make it to the surface again…"

Sans stared at her. She held out her arms, inviting the blow she knew would follow. This was definitely a different person. And if what they were saying was true, and he felt like it was… he had to kill her. He had to kill her before Chara regained control and reset everything.

And that's what he did. He aimed all four Gaster Blasters at her, and four wide, impossible-to-dodge beams were shot at her. Her HP quickly drained to zero. And for the nineteenth time, Frisk's soul shattered at the hands of Sans.

* * *

Frisk awoke, feeling vegetation surrounding her. The flowerbed, she was back to the flowerbed. She was back to the Ruins… and that meant…

She immediately jumped to her feet. She looked around the room, scanning every inch and corner for Chara… but she wasn't there. And it didn't feel like she was trying to regain control like she did when fighting Sans…

Sans. She had never seen him without a smile before, but that… that was utterly awful. He was in pain, she could tell… The death of his brother, his friends… And knowing that one day he'd have to watch all over again… She couldn't imagine having to see what she saw time after time after time…

"Howdy!"

Frisk turned around, seeing a sunflower with what she knew to be a deceitful smile on his face. "I'm Flowey! Flowey the Flower!" Then his eyes narrowed slightly, analyzing her face. "You… You just reset."

Frisk blinked. How did he know? Then it occurred to her: he probably knew the same way that Sans did.

"You reset from that fight… where you overpowered Chara."

"H-How do you know that?" Frisk asked, taking a few steps back.

Flowey smiled. A tattered, black rectangular box appeared above his head, a save point in front of him. _Save File 1,_ it read. "I had to get your save file from her… She's not the same…" He looked down. "So… you can go back to surface now. Everyone, except for maybe that smiley trash bag, will forget about what just happened." He looked up for a second, giving a weak smile. "Hey, and don't worry about Chara, okay? I've got her under control." Frisk smiled. He still had his soul. She gently grabbed one of his leaves. "Hey… what're you doing?"

"You deserve a happy ending, too," Frisk said happily. She pressed _load file_ , and the beautiful sunset of the surface appeared in front of them. Papyrus, Sans, Undyne, Alphys, and Asgore had already walked off; she could see them in the distance. She couldn't help but grin; they were alive.

"Thank you," Flowey whispered softly, gazing into the sunset.

Frisk sighed, partially out of happiness and partially out of relief. She finally got her happy ending back.


End file.
